A device of the initially mentioned type is known. In this device, a plurality of pressure-sensitive sensors are combined or arranged line-by-line and column-by-column on a carrier, each pressure-sensitive sensor consisting of a membrane cell. Neither the carrier nor the sensors are arranged at the test location but it is necessary in each case to connect the test location via one hose each to the respective membrane cell. At the test location, the test object has a small hole in the corresponding surface from which the respective pressure is guided via one hose each to the sensor proper on the carrier. The carrier with the pressure-sensitive sensors can also be housed in the model to be examined, which then provides the advantage that the hose lines are possibly greatly shortened. However, this arrangement is possible only if it is permitted by the model's space conditions. If these space conditions are too restricted, the only choice is to accept longer hose lines and to arrange the carrier with the pressure-sensitive sensors outside the model and the test system which, in turn, creates the problem of passing the hoses from the test location thru the test system. The arrangement of the small holes in the surface of the test object at the test location can modify the surface of the test object in such a disadvantageous manner that the variables to be measured, that is to say the pressure or the variation of pressure with time is distorted merely by this factor. Due to the necessary hose lines, however, the possibly rapidly variable pressure characteristics are greatly affected in any case so that a measurement is possible only under restricted conditions and with great effort. In the arrangement of several test points in the surface of the test object to be examined, using the hose lines for passing on the pressure and the hose lengths possibly varying, it is necessary in every case--provided it is not steady-state pressures which are being examined--to take into consideration transfer functions in the measurement in order to be able to conduct any valid measurements at all. Although these known devices allow pressure measurements to be evaluated at several test locations, they are encumbered with the uncertainty of faulty measurements caused by transmission in the hose lines and also do not represent a solution of how to shape the surface of the test object at the test location without negatively influencing the flow.
On the other hand, it has been attempted to miniaturize pressure-sensitive sensors in single-component construction or single arrangement in order to be able to place the sensor closer to the test location in this manner. The smallest pressure-sensitive sensors have a diameter of less than 1 mm with a length of approximately 20 mm. They have an edge beading which, if it is arranged in the surface of the test object, also disturbs and distorts the flow. Despite this arrangement relatively close to the test location, the membrane contained in the pressure-sensitive sensor is arranged behind a cavity and still at a certain distance from the test location. The arrangement of the cavity brings with it the risk of resonance. A further disadvantage of these miniaturized pressure-sensitive sensors must be considered to be the fact that sufficient installation depth must be provided for the distance to which they extend in the model, which is not always the case, for example with thin carrying wings. Since the pressure-absorbing membrane is not arranged in the surface at the test location in this case either, disturbances and faulty measurements result especially with rapidly varying pressures. In addition, these miniaturized pressure-sensitive sensors are very expensive, which already prohibits a multiple side-by-side arrangement in the surface of a test object.
It is also known to arrange individual piezo elements, that is to say crystals which cause electrical charges to be generated at their surface with deformation caused by pressure, in the surface at the test location for the purpose of measuring pressures. In this case two lines must be brought from the individual piezo element to a charge-sensitive amplifier so that the test signal can be further processed. If several piezo elements and lines are arranged to lie close to each other the output signals varying with time interfere with each other because the lines have high impedances. The individual signal can then no longer be associated alone with the individual test location.